Separate the yolks and the egg whites.
Use an electric beater to mix the egg yolks with icing sugar.
Add the room tempered butter.
Add the bourbon vanilla.
Also add the lemon peel. Stir. Now you add the flour and baking powder as well.
My batter ended up more like a dough so I added some freshly squeezed lemon juice and some milk, perhaps 50-75 milliliter. Then I added the whisked egg whites.
As gently as you can fold in the egg whites.
Spread out the batter in a greased cake pan.
Use enough plums to cover the batter.
The plums were so ripe that I just "teared" them apart and put them on top of the batter. Less ripe plums need to be cut in half.
Cook in the oven for about 40 minutes at 175 degrees C.
Once done, let it cool. You don't need anything extra but if you wish, serve it with whipped cream. Even if the plums are a bit sour I think it becomes too sweet to serve with ice cream/vanilla sauce.
Before serving, dust it with icing sugar.